The report raises concerns about “high-risk” practices such as “chemsex,” sex between men that occurs under the influence of drugs, dating apps, unprotected sex and people seeking HIV-positive partners.

Gay men were disproportionately affected, the report says. The demographic, which represents about 2 percent of the total London population, accounted for 90 percent of new diagnoses in 2015, or 2,406 cases.

There were a total of 2,811 cases in London in 2015, representing a rate of new infections of 32.9 per 100,000 people - five times higher than that of any other region in England and three times higher than the rate for the country overall.

The infection was diagnosed in all London authorities, with the highest numbers in Lambeth, Southwark, Tower Hamlets and Westminster.

The number of cases among heterosexual men and women has risen slightly.

Syphilis is a sexually-transmitted infection that causes highly infectious sores and can go on to cause serious conditions such as heart problems and central nervous disease, and in extreme cases prove fatal.

“Worsening sexual health remains one of the biggest public health concerns facing London and it is worrying to see such alarming rises in syphilis year-on-year,” the regional director for PHE London, Yvonne Doyle, said.

“Although diagnoses among heterosexuals in the capital are more stable they too continue to be higher than we would like.”

Dr. Patrick French, genitourinary medicine consultant at Central and North West London NHS Foundation Trust said: “When I started working in sexual health in London we might have diagnosed four or five people with syphilis in a year - we can now see that number of people with syphilis in a day or two.

“The increase we are seeing in syphilis and other sexually-transmitted infections is a marker of a more general problem within sexual health, and tackling this must be a priority across London.

“More awareness is needed about STIs, how they can be prevented and why it is important to have a checkup if you think you are at risk,” he added.

“Anyone having sex with a new or casual partner should always use condoms and have regular sexual health checks.”

Although most cases of syphilis are treatable with antibiotics, people can be infected and not show symptoms.

Primary syphilis often emerges after three to four weeks with a painless ulcer or rash on the genitals, rectum or inside the mouth. Secondary syphilis causes fever, headaches and night sweats.